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Common Core Math2nd GradeOperations & Algebraic Thinking

2.OA.2: Add and Subtract Within 20 Fluently

Also written as 2.OA.B.2 and CCSS.MATH.CONTENT.2.OA.B.2 · Cluster: Add and subtract within 20.

Make a Facts-to-20 WorksheetAll 26 2nd Grade Math Standards

The Official Wording

Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers.

Common Core State Standards, Grade 2, Operations & Algebraic Thinking · Read it at the source · Checked October 14, 2026

What 2.OA.2 Means in Plain English

Second graders answer 8 + 7 or 15 − 8 in their head within a few seconds. Strategies carry the load: make a ten, use a double and one more, or read subtraction as a missing addend. By June the sums of two one-digit numbers are simply known.

Fluency here is what makes 2nd grade’s bigger work possible: every column of 47 + 38 is a fact within 20 (2.NBT.5). In 3rd grade the same push for memory moves to multiplication, where students know the one-digit products by heart (3.OA.7).

2.OA.2 I Can Statements

  • I can add and subtract within 20 in my head.
  • I can make a ten to solve a fact like 8 + 7.
  • I can say any sum of two one-digit numbers from memory.

2.OA.2 Worked Example

One addition fact and its partner subtraction fact, solved the way a fluent 2nd grader thinks rather than counts.

Problem

Solve 8 + 7 in your head, then 15 − 8.

Make a ten, then run the fact backwards
  1. Start with the bigger addend. 8 needs 2 to make a ten, so take 2 from the 7.8 + 7 = 8 + 2 + 5
  2. Now it is a ten and some more, which is easy to see.10 + 5 = 15
  3. For 15 − 8, think of the addition fact you just used: 8 and what makes 15?8 + ? = 15
  4. Count up from 8 to 10, then from 10 to 15: 2 and 5 is 7.15 − 8 = 7
Answer8 + 7 = 15 and 15 − 8 = 7

Check it: The numbers 7, 8 and 15 belong to one fact family. If 8 + 7 = 15, then 15 − 8 must be 7 and 15 − 7 must be 8.

Common Mistakes with 2.OA.2

Counting all from one

For 8 + 7, counts 1, 2, 3 ... up to 15 on fingers every time

Try this: Teach counting on from the bigger number first, then make-a-ten, so the student has a strategy that is faster than fingers.

Subtraction as a separate world

Knows 9 + 6 = 15 cold, but 15 − 9 is a long count back

Try this: Write every subtraction as a missing-addend question, 9 + ? = 15, until the student reaches for the addition fact automatically.

Doubles plus one, off by one

6 + 7 = 12 because 6 + 6 = 12

Try this: Say the double aloud, then add one more: 6 + 6 is 12, and one more is 13. Fingers on the extra counter help.

Where 2.OA.2 Fits

Comes Before1.OA.6Add and subtract within 20 with strategies like making ten, and know sums within 10 from memory.
Alongside2.OA.1Word problems within 100 that lean on these facts.2.NBT.5Add and subtract within 100, where every column is a fact within 20.
Comes Next3.OA.7Multiply and divide within 100 fluently, knowing one-digit products from memory.3.NBT.2Add and subtract within 1,000 fluently.

Practice 2.OA.2

Addition Worksheet GeneratorFree ToolSums within 20 with an answer key. Mix the facts so students cannot ride one pattern, and ask them to circle every pair that makes ten.Sums to 20Mixed factsAnswer key
Make a Worksheet
Subtraction Worksheet GeneratorFree ToolDifferences within 20, for the missing-addend habit: next to each one, students write the addition fact that solves it.Within 20Mixed factsAnswer key
Make a Worksheet

Quick Check

  1. What is 9 + 6? Say how you know without counting.
  2. What is 14 − 6?
  3. Jamal knows 7 + 7 = 14. How can he use that to find 7 + 8?

2.OA.2: Other Names

2.OA.22.OA.B.2CCSS.MATH.CONTENT.2.OA.B.2

Common Core State Standards © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved. Official wording from the Common Core State Standards PDFs at corestandards.org, last checked October 14, 2026. The explanation, I can statements, example, mistakes and practice on this page are EMStudio’s own, written beside the official wording. They are not part of the standard.